In an integrated circuit device formed by mounting an LSI (Large Scale Integrated circuit) or other active circuit element on a printed wiring board or other wiring substrate, calculations are performed by the transfer of electrical signals between the LSI and the outside, and/or between a plurality of LSIs connected to each other. A direct-current power supply voltage must always be supplied to the LSI in order for such an integrated circuit device to operate.
FIG. 24 is a schematic diagram showing the LSI and the power supply circuit of the printed wiring board in an integrated circuit device. As shown in FIG. 24, power supply wiring 101 and ground wiring 102 are usually provided to the printed wiring board, and an LSI 103 is connected between the wiring units. A power supply regulator 104 is provided for supplying a power supply voltage to the LSI 103 by applying a power supply voltage VCC to the power supply wiring 101 and applying a ground voltage GND to the ground wiring 102. Furthermore, a capacitor 105 is provided in the vicinity of the LSI 103 as a charge supply source in the printed wiring board for instantly supplying a charge to the LSI 103 when the LSI 103 is operating. In the printed wiring board, the power supply circuit is formed by the components relating to the power supply for the LSI 103, i.e., the power supply wiring 101, the ground wiring 102, and the capacitor 103. Besides these elements, an inductor and a filter (not shown) are also sometimes provided to the power supply circuit in order to prevent the expansion of high-frequency noise that is outputted from the power supply.
FIG. 25 is a graph showing the fluctuation of the power supply voltage that occurs when the LSI is switched, wherein time is indicated on the horizontal axis, and the control signal level and the power supply voltage that are supplied to the LSI are indicated on the vertical axis. The switching time is the time at which a control signal level of some kind for controlling the operation of the LSI is switched to switch on operation of the LSI, and the switching time is mostly synchronized with the rising time and the falling time of the clock signal. In the integrated circuit device shown in FIG. 24, the necessary charge is fed mostly from the capacitor 105 when the LSI 103 is switched. However, since the capacitor 105 has a limited capacity, and the drive capability of the power supply regulator 104 is also limited, the power supply voltage fed to the LSI 103 fluctuates as shown in FIG. 25 when a large amount of charge flows from the capacitor 105 to the LSI 103. When the maximum fluctuation ΔV of this fluctuation is larger than the allowable range of the LSI 103, the LSI 103 malfunctions, and malfunctioning can occur in the entire integrated circuit device.
Recent increases in speed and density of integrated circuit devices, as well as increased complexity of the functions of the electronic devices in which integrated circuit devices are mounted have been accompanied by an increased variety of power supply voltage values for the LSIs that constitute digital circuits, and the amount of charge needed for operation has also increased. In order to satisfy these demands, numerous limitations have been placed on the structure of power supply circuits, and particularly on the power supply wiring and ground wiring of printed wiring boards, and the arrangement of capacitors, inductors, and filters. The design margins in power supply circuits have also become extremely small. As a result, the time needed to design the wiring of power supply circuits has increased, and once the power supply circuit is designed and the integrated circuit device is fabricated, it is often the case that the electrical characteristics required in the integrated circuit device cannot be satisfied and there is no alternative but to redesign the circuit. Problems result in that an extremely long time is taken to design the integrated circuit device.
In order to overcome the problems described above, a technique has been developed for computing the fluctuation ΔV of the power supply voltage in the design stage of an integrated circuit device. This technique makes it possible to design an integrated circuit device in which the fluctuation of the power supply voltage is within the allowable range without actually fabricating the integrated circuit device, by appropriately computing the fluctuation of the power supply voltage while the integrated circuit device is being designed, and redoing the design when the fluctuation ΔV exceeds the allowable range. For example, Non-patent Document 1 discloses a technique for computing the fluctuation of the power supply voltage by using a three-dimensional electromagnetic analysis means to simulate the power supply voltage behavior of the integrated circuit device over time.
[Non-patent document 1] Jiayuan Fang, “New Methodologies for Signal and Power Integrity Analysis of Electronics Packaging,” 16th Annual Meeting of the Japan Institute of Electronics Packaging, 19B-01, pp. 151-152.